The phase diagrams and electron orderings of the half-filled extended Hubbard models with anisotropic spin-exchange interactions are studied. The cases of ferromagnetic and antiferromagnetic exchange couplings are considered for repulsive on-site interaction (U ? 0). The analysis of these t-U-J||-J??models is performed for d-dimensional hypercubic lattices including d = 1 and d =??by means of the (broken symmetry) HFA supplemented, for d = ?, by the slave-boson mean-field method. The basic features of the derived phase diagrams are discussed.
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The properties of the half-filled Kondo lattice model with anisotropic intersubsystem exchange interaction JXY and JZ are discussed. The phase diagram and ground state characteristics of the system are determined within a variational mean-field approximation for the case of rectangular density of states (DOS) for itinerant electrons. The ground state phase diagram is found to exhibit five different phases: Kondo singlet state, two planar antiferromagnetic phases, and two Ising antiferromagnetic (Néel) phases.
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